Are bridges for cars built as strong as bridges for trains? We have the equivalent of small trains on our roads and bridges daily. Were they built for the load of a rig with three trailers? I know that some smaller bridges certainly are not. I doubt that any could take this abuse unless they were built like the old London Bridge.

I agree. When we get those heavier loads on the bridge it just can not take it and the fact that mndot said the lack of repair was not a money issue is a load of ****. If they had the money why would they put off repairing the bridge until the last minute when they are too late and now they need to not just repair but replace the bridge.

We are so sad for those on the bridge, and for those that love them. Our lives are precious. It reminds me to be kind every day - to be patient and caring. We just get so busy, we sometimes forget. Peace to everyone in the Twin Cities.

The bridge collapse is a reminder of the faulty prioritization of our government. We have incredible technological advances, but when all is said and done...it is about the money. We have big business buying off our politicians drowning them in special interests legislation...it takes a devasting tragedy such as this to get Bush to turn his attention to what is happening on our soil.. I am so sad for those lost in this horrific event. Our prayers go out to them and their families.

Does anyone here wonder why the engineers didn't look after this bridge? Maybe it was because they had to focus on the construction going on the highway, I don't know. But honestly; the bridge barely passed the reinforcement tests it was given. If there was such a small margin between passing and failing on something as important as a highway bridge, don't you think the engineers (or the government, for that matter) would be concerned about it?

We all feel great sadness for those who were on the bridge when it collapsed and hope those who were only injured are doing better and be home to there families soon. We should know now that we should be kind to people ( extra kind ) to people we know who have family who were on that bridge. I believe all of this could have been stopped in a way. Give your prayers to those in this tragic accident.

Like most others, I've been garnering all the information about the bridge structure itself that I can find.
I have found nothing that indicates that MnDOT put off repair work because of lack of funding.
From what I've been able to find, they have not put off repair work at all.
There was a consideration of installing gusset plates over a number of areas that had shown signs of stress cracking. However, the cracks had not migrated at all over a period of years. They were being watched carefully. Originally, the state planned to install these plates. However, after more study decided it was a dangerous thing to do. They would be moving into unknown territory, and were worried about the thousands upon thousands of holes that would be drilled to mount these plates causing new stress points. This could be a very real concern.
They decided instead to continue to monitor the existing cracks carefully while outside engineering companies study further the idea of the gusset plates.
I can only assume that these plates are what many think were put off due to money. Nowhere have I been able to establish money as being a factor in the decisions of the engineers involved in this.
One other thing some may have missed is that though the bridge was considered structurally deficient, this does not mean it was considered dangerous.
Had inspectors found anything that was cause for immediate concern, the bridge would have been restricted to traffic levels or, if bad enough, closed. Anyone who thinks the state or federal governments would have callously just kept it in service while knowing it could go down at any moment needs some better insight.
We need to wait until all the data is in, and the findings are made. We might all be surprised to find that the collapse was not caused by one simple event, but rather by a series of small things, unnoticed and not anticipated by anyone, that all contributed to the failure.

Instead of focusing on saftey issues, the government is more worried about making sure that the twin cities looks nice for next years republic covention (check out the display on pigeon pop in the museum) and other not as important items. the 35-w collapse may have not happened if we didn't overlook everyday items that might need repairing or need to be rebuit.

The 35W collapse could have been avoided entirely. engineers said that over 40 years ago (or something like that) was deamed structully deffiecent yet the government didnt close the bridge saying that it was ok. that makes u think about othert bridges

In 1974, I lived at 600 University Ave. when I attended the UofM. To cure my loneliness I often walked down along the river under Bridge 9340. I would look up in awe, pondering the close packed atoms of iron held together by busy little electrons with atoms of carbon every so often to keep the iron layers from slipping: the magic of steel. The photos don't reveal the scale of this bridge. Clearly steel was a more efficient material than the amount of concrete poured for the 10th Ave. bridge alongside, but something bothered me about it even back then. Like an ant scaled to the size of an elephant, there was a spindly nature to it, something skimpy in its construction. Never did I imagine the object of my attention would be lying in the river some 30 years later. Back then I was simply in awe the structure could be accomplished with such economy of material - it's scary.

Bridge 9340 was designed before computers were readily available, before electronic calculators, probably using slide rules. Yet extensive computer modeling using finite element analysis has been subsequently performed yielding analysis that didn't indicate any gross engineering oversights. The structure was basically sound from an engineering perspective. Formations of loaded dump trucks made passes over the bridge and strain gauge measurements indicated forces lower than predicted by the computer model: the deck must be redistributing the load. Yes, the roller bearings were not operating as predicted, many cracks were drilled out to prevent further propagation of a fracture, repairs were made, bolts missing here and there, but the basic structure seemed to have a safety margin of at least a factor of two. No further degradation was being measured/observed. Is it wise to arbitrarily replace a design which is still functioning according to specification? On what basis? Because a single point failure might result in catastrophic collapse?

After the fact, we may question:
What effect did the frozen bearings cause?
Did an extra static load of construction material cause any resonance? (Difficult to significantly increase the weight of 3300+ cu. yds. of concrete deck, however.)
Did the modified traffic pattern (for road work) apply some unforeseen moment to the deck?
Why was traffic allowed to increase from 6 lanes to 8 lanes later on? Was this part of the initial design specification?

Engineers are criticized for throwing either too many or too few resources at a problem. While overkill may be considered safer, the cost is generally prohibitive. No one wants to build something that fails. Known good practice is generally observed. Everyone is trying to do the best they can under the constraints they are facing. I hope there is ultimately no one to blame. While I am touched by the lives of those caught in the cruel web of fate, my thoughts are with the technicians and engineers who failed to adequately predict the unforgiving nature of the materials and design. May they come to forgive themselves for any human failure they bear.

CA, my wife drove over that bridge about 3:30 that day. Close to when you did. Not that it matters.
I noticed today in the news that the Brooklyn Bridge in New York scores lower on that same rating system that scored the I-35W bridge so badly. Yet, it too, is still operating. Note that the Brooklyn Bridge still has most of its original turn of the 20th century parts, including cables.
I notice people are still claiming that the state didn't throw enough money at that bridge. While that could turn out to be true after the investigation is over, at this point it seems silly to throw money at something when you don't know just where to throw it.
The state had a plan for that bridge, and that plan was based on solid engineering and seemingly good inspections. That bridge, for whatever reason it came down, did not come down simply because it was worn out and decrepit.
It was not.
Something happened that none of use has a grasp on at this time.

I think that there must have been a weakness in the bridge somewhere for it to give away. I am saying all the time that they do not make things like they used to. In the older times everything lasted forever. Nowdays, you lucky if it lasts until you get it paid for. I just am so sorry for all the people and their families. God bless them.

I have a Ph. D. in physics, but no specific background in Civil Engineering. I take an informed layman's interest in events of this type, such as for example the Challenger and Columbia shuttle disasters. In this case I have reviewed some of the background material in the Wikipedia references, and of course viewed videos, photo albums, and commentaries pertaining to the collapse of the I-35W bridge.

My first impression is one shared by many who have commented on the "surveillance video" which seems to be the unique record of the collapse of the main span. That is, that the collapse was initiated at the southern end of the main span. In the video, we see the main span in free fall while it is still attached to the north pier.

Then, from news footage of the south end in the collapsed state, it seems evident that it was the site of the initial collapse, since it fell to the side. From the video, we saw that the north end collapsed in a logical and symmetrical order from the stresses induced by the fall of the main span. What then could have induced the truss above the southern end of the main span to fall to the side? It must have been the initial failure.

Yet, I saw in the news that the southern end had been "ruled out" as the cause of the collapse. My belief is that this is a reflection of the usual ignorance and carelessness of news reporters, and that they were told by investigative authorities that the asymmetry of the collapse at the south end did not necessarily mean that the collapse started there, and so said it was "ruled out".

Of course, the investigative authorities are bound not to give any hint of a conclusion before the Investigation is complete, some 1 1/2 years in the future, but anyone of a curious bent and any kind of technical orientation will naturally race ahead in his own mind as he digests the available information.

I feel the official reticence to come to a conclusion is reflected in the inspection reports and studies that one finds in the Wikipedia reference section. There is a pdf of a report from 2006 that was chartered by the Minn. DOT to recommend enhancements or repairs to the bridge. This report catalogs in the most unjudgemental terms conditions which ought to raise the hairs on anyones neck. I speak of the condition of the "roller bearings" on the main support piers at the south end of the main span. These are very strange looking affairs, being a set of four rollers, like "rolling pins", arrayed between two plates at the top of the concrete pier. These are supposed to allow the bridge supports to move by a few inches in response to thermal expansion, and variation in load. The report mildly comments that they are not functioning, and that they are covered with rust, debris, and multiple coats of paint! The response to this state of affairs is to adjust the input to their computer model to account for a FIXED pier bearing .

These roller bearings are a major feature of the bridge design, as as obvious simply from the effort and material that was devoted to them. That their dysfunction was accepted and accounted for as a simple alteration of the computer model of the bridge tells me all I need to know about "why the bridge collapsed".

Yes definitely, I too believe that the initial failure/displacement occured in the first span of the main southern cantilever truss . Because of the distribution and location of the fallen main steel and the detachment and distribution of the pcc deck structure my "wild guess" is that the main cantilever truss superstructure had developed a small discontinuity at or near the top of the eastern column of the main span southern pier. This gap "worked" (opened and closed for a while). Finally the east side of the main truss superstructure broke at or south of the southern pier's east column. Then the truss superstructure sagged to the east and twisted clockwise over the 2 columm southern pier. I believe this collapse path is what caused the nothern pier to be visibly displaced southward by the falling main span.

"The response to this state of affairs is to adjust the input to their computer model to account for a FIXED pier bearing."

Yes, this was likely the major oversight. The rollers were not rolling appropriately, but neither were they fixed. One report from around 2003 noted that when the span was expanding due to temperature, the sticking rollers might cause the bridge to make "sharp, quick" adjustments rather than the continuous adjustments intended. Sharp, quick adjustments are a very bad thing in a structure of this kind, and it is likely that one of these sharp expansion adjustments took place on that very hot day that the bridge fell.

That expansion adjustment was probably a very large one, due both to the heat and sunny weather and the extra weight on the bridge. Additional load makes it harder for the rollers to roll, so the tension has to build higher to move them. The dead load (the weight of the empty bridge) had already been increased by about 25% over the years by adding the extra 2" layer of concrete, the new railings (while keeping the old ones), and the concrete median. On top of this, on the day of the crash the bridge was bearing a concentrated load on the center span due to construction materials piled there that were intended to be spread out over the entire span eventually. This construction material was not a risk in terms of its weight on the structure, but in terms of its weight on the rollers. The harder it was for them to adjust, the more potential energy the span had to build up in order to move them, and the larger the resulting "sharp, quick" adjustment. Once the bridge made a sharp adjustment that was not modeled in any earlier simulations, a number of points could have failed, including the gusset plates identified by the NTSB, although that doesn't seem to explain the tipping of pier 7.

Anonymous, you have it pretty well, in my opinion.
But I suspect that we'll eventually learn that the collapse was caused by more than one thing that happened at just the right time, combining to cause the bridge to fail.

On the media, right on.
Here's something a friend emailed to me that some might find interesting. It's long, but number 3 is especially interesting regarding bridge design;

This is a complicated matter, so please bear with me.

1) There is no single factor of safety applicable to the bridge as a whole. Bridges are complex structures and stuctural elements warranting individual design calc's will have separate factors of safety. Most elements will need to be designed to code, or to the specifications of the authorizing agency, in which case the factor of safety will be dictated. That does not relieve the designer and approving agency from exercising more rigorous standards. Those more rigorous standards differ from area to area, based on standard practices applicable to the area. For instance, an area subject to frequent seismic activity will differ from those in say North Dakota.

2) Unfortunately, cost is a factor, and some ultra-conservative factors of safety simply aren't feasible. Years of experience, along with state of the art design techniques, are used to determine what is a reasonable expectation for safety. For instance, the people through their local flood control boards were ultimately responsible for deciding not to spend the money to improve the Mississippi levees in New Orleans to withstand a greater than catagory 3 hurricane. Essentially, the same thing happens with highway construction dollars.

3) There is always the rule of "for every benefit, there is an offsetting disadvantage." For instance, shorter spans could be structurally more sound, but that may require an increase in the number of support columns. More columns in the same area heightens the likelihood that an out of control vehicle will hit one. In the design of a bridge the combination of effects is nearly endless. Suppose one increases the material at a joint to make it stronger. That would add more weight at that location, which causes an increase in reinforcing material, which in turn may make the structure heavier and more rigid. A seismic event would result in increased swings in loading on the stucture due to the extra weight, along with less of an ability to "give" during movement due to increased rigidity. The result is that the structure may actually reach its "inelastic limit" more easily, and a catastrophic collapse would occur more readily. A "lesser" design may allow for more distortion under movement before failing.

4) A structural design does not just address failure limits, but may include failure mode analysis, as well. Take the example of a high-rise building like the World Trade Center towers. If a failure should occur, you would like to control the damage. The building is therefore designed so that the interior supports will fail before the outer corner supports. The idea is to keep a part of the building from separating and falling on an adjacent structure. The failure would tend to be contained within the footprint of the structure. A clever enemy could design a method to create a complete failure of all structural columns in the center of the building (by, say, crashing a plane loaded with fuel, using the hydrostatic shock of the fuel to knock out the columns, kind of like a liquid explosion). Then a fire, weakening the beams supporting the structure above could cause a dramatic collapse of the floors above. Because of the design, the affected floor would "pancake" instead of shedding weight off the side of the building. If the "pancaking" included enough weight (and remember it is being directed toward the center of the building), then the inelastic limit of the structure below would be exceeded immediately, resulting in the "pancaking" of that floor. A chain reaction would have been started. The point I want to make is that bridges are designed to have particular failure modes. In general, the idea is to produce a noticeable deformation, prior to a catastrophic failure. Inspection regimes are designed around this idea. Some briges have built in sensors to measure deformations.

5) As part of the failure considerations, the design engineer specifies an inspection regime. The engineer knows the structure will not last forever, so he designs elements to show problems where he can, and to provide for maintenance on a schedule. The scheduled inspection and maintenance are an element of the "factor of safety" equation.

6) The ultimate factor of safety of any given structure does not just depend on the design engineer and maintenance. All can be for naught, if there is not adequate construction techniques used and material quality monitored. Therefore, construction management is an incredibly important factor in the lifetime safety of any given structure. Do you remember the Hyatt Regency disaster in Kansas City about 30 years ago? It turns out that an unanticipated failure of communication in the approval of structural shop drawings resulted in a very minor change in the specification of a fastener. Over time, the fastener worked loose, allowing the suspension element to fail, which allowed an overload of the structural design of the mezzanine. By an incredibly bad turn of luck, this occured at a time when the mezzanine was at its maximum anticipated traffic load, which caused the deformation of the system to exceed the catastrophic limit before anyone could react.

7) As to the design allowing the segments to "come apart," the reason was simple. Minneapolis experiences wide ranges of temperature. As a result, bridge spans must be designed to allow for a great deal of expansion and contraction. The segments cannot be tied together, but rather only certain types of movement are allowed. The supporting structure supports, of course, but allows the movement of segnents with respect to one another. Undesirable movement is controlled by structures that are designed specifically for a particular type of movement. Because the structure needs to react as whole, the restricted movement on one section depends upon similar elements on adjacent spans. The result is expansion and contraction, though freely allowed, is limited to location that keeps the span on its support. If one span or support fails in such a manner as to no longer constrain the limits of movement in direction that expansion and contraction is allowed, then the adjacent span may be allowed to move sufficiently to come off its support. When that happens, the next span becomes unconstrained on one end, and it can exceed its movement limits, etc. Of course conditions are such that the effect tends to lessen the further you get from the initial failure, until one span in the series no longer moves enough to drop off its support.

Regarding a mechanism to "catch," it is not feasible to design a whole additional structure to catch a bridge deck. However, if you will remember the design, the concrete columns were topped by elaborate steel structures. Those structures are designed to "catch" the span in the event of a failure, by considering the amount of reactive movement that might occur and size the support accordingly. But if you will remember, the south support steel was completely mangled, and the constraint at that location did not exist. The intact stucture on the north side did in fact prevent the collapse from continuing northward.

This is just a "quick and dirty" explanation of generalities. It probably applies to the bridge in question, but please remember that every instance will have its own peculiarities.

Oh my gosh! i was so shocked when i heard about the bridge collapse. What scared me most was that, that bridge is 1 mile from where my family is, and my cousin crossed that bridge 2 minutes before it collapsed. It's so scary that things like that can actually happen.

I live almost 70 miles from that bridge but I, too, was shocked. I used to drive over that bridge fairly often. At least twice a week. Not nearly so often as some, but often enough. I've been driving on it with some regularity since about 1997. Before then, it was sporadic.
Over the past ten years, I can recall a number of times when traffic was slowed due to closed lanes for bridge maintenance. So I can say that it did receive maintenance.

One thing we often forget about life is that there is no absolute guarantee of safety in any part of our life. There is a very thin line between what we perceive as safe, and utter chaos. We always expect our technological advances to protect us, and keep us from having to take our own safety precautions. All we need do is remember the Titanic disaster in April of 1912. By all the standards of the day, that boat, and it's sister Olympic, represented the highest technological achievement in maritime safety. It had all the safety bells and whistles, including long range radio, and an underwater listening device to locate bouy's in darkness or fog. (Radar was decades away still)
It had watertight compartments that should have kept the vessel afloat in the worst imaginable accident.
But it wasn't enough. We all know the story.
The point is that we should not expect the neat devices we build to enrich our lives to always function perfectly and keep us safe from all harm.
From the Titanic disaster, we learned a lot and new safety procedures were instituted to ensure this particular thing would not easily happen again.
This bridge should also be a lesson to us all. What that lesson will be remains to be seen, and we won't know until the investigation is complete.
Still, one lesson is that none of us is ever REALLY safe at any time. We all know that, but we tend to forget it.
Mark

I am almost 12 and I used to drive on the bridge all the time and about that time it fell we were going to go see some old friends over that bridge but we had to take my cat to the vet real quick and so we did not go on it. I think we may have been saved because we did not go over the it. I am also very sad because of the people who died.

my brother had a sleep over with one of his friends the day the bridge collapsed. And lucky he did because if he didn't his friends dad would have been on the bridge. thank goodness for Robert!!!!!!!!!!!!!!!

I have serious doubts concerning the National Transportation Safety Board's assesment that the problem occurred in the so-called gusset plates. That these plates were lacking the metallic girth to sustain the remainder of the bridge's structural integrity seems to lack complete truthfulness. It is as if washers were incapable of keeping the bridge together would be the argument. Considering that the bulk of the attention placed by the bridge's contractors at the time of construction(in the '60's) seem to suggest to me that at that time, overkill would have been built into the safety of that structure. Gusset plates, therefore, seem to me an inadequate explanation. Granted, these would have stress fractures given their being conjoined as these were, but the photos seem to convey that the bridge "jumped" its footings which would suggest that gusset plates in themselves would be incapable of restraining this process from having occurred.

I think this is a good web site about scienc facts and the new about the bridge it even help me with my homework sometiems this is a good way to study about the new you all should even get infomation about coloning cows to produce more milk you see I don't think it's safe to do that because you could die if you got posined or somthing you know what I mean!!!!!!!!!!!!!

I think it was pretty sad. I haven't felt that bad since the world trade center attack. And it was in my home town. I think people should take in consideration that other people need to live. And if we commute on a bridge that mug better be safe enough to go on ya dig?

i think that this was a very bad situation that happened to everyone. i think that the government is responsible for alot of the stuff that happened that day. they are building everything to fast. if they took their time to do things they wouldnt have this problem.

I was coming home from dance when I heard that the bridge had collapsed. My mom was devastated, but I didn't know why. Then I found out which bridge it was, and I was suprised. I thought, "Wow! A bridge that big collapsed?" I could not believe it! When we got home, I sat down and watched t.v. with my dad. The pictures and stories were unbelievable! It was awesome! (Not in a good way, though.)

It is good to read about the problems people think caused the collapse. Ever since moving to Minneapolis I think twice about every bridge I drive across. How come it hasn't happened to other bridges in the world?

When I first heard about the collapse of the 35W bridge I was in the car about to go on it. When my mom called and well told me the story. It was a bit freaky but I'm glad it didn't come to worse. It's something that most people don't think could happen but now it's something most people are scared of.

I think its terrible that the bridge fell at no warning. The odd thing is that my dad and my cousin were coming back to South Minneapolis and passed the bridge about 15 minutes before it fell. at that same week my dad told me that as soon he left the bridge heb felt that the road felt suspicious.

like many minnesotans, i will long remember the day of the bridge collapse well.
i was home and just finished watching 'the simpsons' and my dad calls me asking me about this news story about a minnesota bridge that had just fell. i asked 'what bridge?' then it prompted me to turn the t.v. back on and i saw it, i thought it looked like an earthquake had hit! what i saw reminded me of the 1989 world series earthquake in san francisco, as 2 bridges fell because of it.
like many twin citians, i've driven over that bridge many times before. while the odds weren't high that i would be there when it collapsed, what bothered me was the randomness of it. 13 people died, and it didn't have to happen!
it was a night where i got way more calls than normal, from friends and family wanting to know if i was all right. i got 4 calls if you count one friend that i called a day later, who had said he tried to call but the line was busy.
the thing i didn't care for was what happened after it, how there seemed to be too much finger-pointing and not enough energy devoted to just getting the job done. but this is typical in tragedies, how there always will be finger-pointing, since it didn't have to happen.
the most lasting impression may have been the cartoons i saw a few days later, one had a map of the country and each car had a word balloon saying 'i hope this bridge is safe'. another did a variation of the license plates, saying 'land of 10,000 TEARS' instead of lakes.

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